the following works. i don't exactly what happens here. I guess "lm"
might treat S1 and S2 as quantitative variables, not qualitative
variables.
cheers,
Zhiliang
S1 <- as.character(Data[,1])
S1 <- as.factor(S1)
S2 <- as.character(Data[,2])
S2 <- as.factor(S2)
data <- data.frame(S1=S1, S2=S2, ExM=Data[,4])
g <- lm(ExM ~ S1*S2, data)
anova(g)
Analysis of Variance Table
Response: ExM
Df Sum Sq Mean Sq F value Pr(>F)
S1 5 4.7454 0.9491 961.66 < 2.2e-16 ***
S2 5 4.9548 0.9910 1004.10 < 2.2e-16 ***
S1:S2 25 1.2993 0.0520 52.66 < 2.2e-16 ***
Residuals 180 0.1776 0.0010
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
On Wed, Jul 8, 2009 at 10:34 AM, Lars
Bergemann<lars.bergem...@hotmail.com> wrote:
>
> Hey!
>
>
>
> Could you please take a quick look at what I have done? Somehow I get wrong
> results using the anova(lm()) combination compared to doing a two way ANOVA
> by hand.
>
>
>
> Running:
>
>
>
> Data<-read.table("Data.txt");
> g<-lm(ExM~S1*S2,Data);
> anova(g);
>
>
>
> Gives:
>
>
>
> Analysis of Variance Table
>
> Response: ExM
> Df Sum Sq Mean Sq F value Pr(>F)
> S1 1 4.3679 4.3679 167.045 < 2.2e-16 ***
> S2 1 0.9427 0.9427 36.053 8.236e-09 ***
> S1:S2 1 0.3231 0.3231 12.357 0.0005371 ***
> Residuals 212 5.5434 0.0261
>
>
> I compared it to the work done by hand, ie calculated all the different
> square sums using sum() and tapply().
>
> So I know that anova(lm()) gets the degrees of freedom equal two 1, 1, 1 and
> 212 when it should be 5, 5, 25 and 180. Also, the square sums are quite
> different ... I get 4.xx, 4.xx, 1.xx, 0.xx ... as you see, what anova(lm())
> gets is different.
>
>
>
> The data: S1 has 6 levels, so has S2. On average, each cell has 6 values,
> most cells have actually 6 values, and there are two of each: 5, 7, 4, 8 - so
> average 6.
>
>
>
> Could you please help me, why it does not work with anova(lm())? I tried
> quite a few thinks found with Google, but it all gave me the same result as
> anova(lm()) ...
>
>
>
> Thanks a lot!
>
>
>
> Lars
>
> _________________________________________________________________
>
>
>
>
> ______________________________________________
> R-help@r-project.org mailing list
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>
>
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